Throughout history, mankind has experimented with various means of improving vision using external devices and instruments. While glasses and contact lenses do provide many people a reasonable quality of life, they do have limitations. For example, for many lifestyles, glasses can be inconvenient. And, for some people they do not give the quality of vision desired.
Contact lenses have addressed some of the inconveniences of glasses. The apparent invisibility of contact lenses has satisfied those who were self-conscious about wearing eyeglasses. In addition, contact lenses have allowed people to engage in activities that were previously either prohibited or difficult to engage in while wearing glasses, such as certain athletic endeavors. Nonetheless, wearing contact lenses does come with a price. In addition to the price of lenses, contact lens wearers must devote a considerable amount of time in maintaining their lenses. In addition, there still are limitations as to the types of activities one can participate in while wearing contact lenses, such as swimming or other water sports where contact lenses can be floated out of the eye. Lastly, long term contact lens wearers may develop an intolerance to wearing lenses or develop long term eye damage.
As a result of the limitations of glasses and contact lenses, ophthalmologists have developed a number of surgical procedures, as which modify the eye itself--to correct the actual cause of poor vision in the first place. One early form of vision correction surgery was radial keratotomy (RK). RK is basically a surgical operation, which can improve myopia (nearsightedness) by flattening the curve of the cornea over the pupil. A surgeon makes several radial incisions in the cornea with a scalpel. These cuts are fairly deep and are designed to cause the central cornea to relax or flatten and the peripheral cornea to steepen, which reduces the dome of the central cornea. This results in effectively modifying the focal length of the eye's lens, allowing light to focus on the retina.
However, RK does have serious shortcomings. First, and perhaps most significant, is that the radial cuts in the cornea are required to be fairly deep. In fact, sometimes these cuts extend up to 90% of the thickness of the cornea. As can be appreciated, the depth of these cuts seriously weakens the cornea, which frequently leads to progressive flattening of the cornea and increasing farsightedness, (the opposite of the nearsightedness the RK procedure was tailored to correct). In addition, RK can only be used to correct low amounts of myopia. Furthermore, it cannot correct hyperopia (farsightedness).
A more recent development in vision correction is a procedure called photorefractive keratectomy (PRK). As with RK, PRK modifies the shape of the cornea to correct vision. However, the process is very different and provides significant improvements in patient risk and correction capabilities. Instead of making SE radial cuts in the cornea with a scalpel, PRK uses an excimer laser to sculpt an area 5 to 9 millimeters in diameter on the surface of the eye. This process removes only 5 to 10% of the thickness of the cornea in mild to moderate myopia and only up to 30% for extreme myopia. The major benefit of PRK is that the integrity and strength of the corneal dome is retained. The excimer laser is set at a wavelength of 193 nm, which will remove a microscopic corneal cell layer without damaging adjoining cells. This allows an ophthalmic surgeon to make extremely accurate and specific modifications to the cornea with little trauma to the eye.
The ability to sculpt, rather than cut, opens up the area for treating a number of vision conditions, including hyperopia and astigmatism.
An even more recent development is a procedure known as LASIK. The LASIK procedure is a hybrid procedure, which involves both a surgical cutting and laser sculpting of the cornea. FIG. 1 shows a normal eye before any type of vision correction surgery is performed. Eye 10 includes cornea 12, which includes an outer layer called the epithelium 14. The epithelium is a protective outer layer of the cornea. With PRK, the epithelium is sculpted along with the remainder of the cornea. However, it is essentially unaltered with the LASIK procedure. The first step in the LASIK procedure is to slice the cornea from the side to produce a corneal flap 16 including the epithelium 14. (See FIG. 2) The flap is cut using a device called a microkeratome. A part of the microkeratome flattens the cornea during the slice so as to create a corneal flap of uniform thickness. The slice is completed before a complete disk is created, which results in a corneal flap 16 of uniform thickness with hinge 18 at one edge thereof. The surgeon then rolls the flap back to expose an inner layer 20 of the cornea 12. With the flap folded back, the surgeon performs the refractive correction on the inner layer 20 of the cornea using an excimer laser in a manner similar to PRK. When the corneal sculpting is complete, the flap is repositioned into its original position and the procedure is complete. The eye has a natural suction facility that retains the flap firmly in place at this time. However, care must be taken by the doctor to insure an excellent fit when repositioning the flap. It is this critical aspect of the LASIK procedure to which the present invention is directed.
Since this portion of the LASIK procedure is critical to the resultant improvement in eyesight, many apparatuses and methods have been developed in order to aid in the precise repositioning and adherence of the corneal flap. Of particular importance is U.S. Pat. No. 5,533,997, which issued to Ruiz on Jul. 9, 1996. The '997 Patent discloses a LASIK procedure especially tailored to correct presbyopia. The '997 Patent discloses that after the laser ablation step of the LASIK procedure is accomplished, the ablated layer of the cornea is exhaustively cleaned using a balanced saline solution, a brush and aspiration in order to assure that the interface is free from impurities, epithelial cells or foreign particles. (Col. 3, lines 38-42) The '997 Patent further discloses that thereafter, the flap is replaced in the bed, adequately oriented in order to avoid altering its natural position. The edges of the flap are then dried using air for several seconds to obtain adherence of the flap. However, the drying step disclosed in the '997 Patent is not controlled. Accordingly, this procedure can result in the dislocation of the corneal flap caused by the air used to dry its edges. In addition, since the bonding of the flap is not controlled, it is tested or verified using tweezers. (Col. 6, lines 14-15). If the flap is not adequately bonded, then the tweezers could reposition the flap, which would require an additional positioning and drying step. The adherence verification method could also lead to damage of the corneal flap caused by the tweezers themselves.
Accordingly, the disclosed invention provides a method and apparatus which can be used in drying a corneal flap during the LASIK procedure, which results in controlled drying under the observation of an ophthalmic surgeon until adequate drying and flap adherence is observed.